The goal of Project 5 is to inform the design of dual compartment microbicide formulations by developing a comprehensive understanding of the user experience, and the impact of that experience on user preferences, product acceptability and, ultimately, product adherence. Project 5 incorporates a series of formative and experimental studies into the overall IPCP dual compartment microbicide development plan. Both men and women will serve as participants. Study 5.1 is a formative mixed methods study, designed to develop RAI (receptive anal intercourse)-specific user sensory perception and experience (USPE) instruments. A set of formulations that represent the range of formulation properties and characteristics believed to be best suited for dual compartment use will be studied. In-depth interviews will be used to generate FRAI-specific items to be incorporated into existing USPE instrumentation. These measures will then be used to evaluate USPE and conventional acceptability constructs with respect to the candidate microbicides being evaluated in Project 4 (USPE studies incorporated into Project 4 referred to as Study 5.2). Finally, Study 5.3 is a randomized trial comparing prototype formulations being developed in this IPCP with respect to USPE and willingness-to-use such formulations. The USPE trial (Study 5.3) will achieve two important goals: 1) psychometrically validate novel and adapted USPE instruments specifically designed for rectal microbicide evaluation, incorporating the current understanding of vaginal USPE into an omnibus conceptualization of dual compartment microbicides, and 2) evaluate users' perceptions and experiences of the physicochemical and rheological properties of rectal microbicide formulations, and how those perceptions and experiences impact conventional acceptability and willingness-to-use variables. By understanding the correspondence between the user experience and preferences, we can better inform formulation design. This knowledge, in combination with the optimization of formulation for delivery of the active pharmaceutical ingredient, will positively impact effectiveness by increasing the likelihood of the microbicide being used as intended, thus contributing to decreases in HIV incidence in those at-risk.